Published research shows that the synthesis of glycogen in animals takes place either directly from glucose in the liver, or, indirectly (the glucose paradox) from glycolytically produced lactate which has been transported to the liver from peripheral tissues. This project will seek to determine whether these direct or indirect pathways of glucose and glycogen formation are affected in endurance trained animals by comparing them to untrained animals. The aims are: (a) to measure the relative contributions of the direct and indirect pathways to glycogen synthesis, (b) to determine the effect of endurance training on these pathways, (c) to determine the effect of endurance training on gluconeogenic rates under both resting and exercising conditions, and (d) to assay the activities of the glucose phosphorylating enzymes hexokinase, glucokinase and glucose-6-phosphatase. To measure these aspects of carbohydrate metabolism and blood glucose utilization, experiments will be conducted with trained and sedentary rats in a metabolic chamber where 02 and CO2 will be monitored. Animals will be infused through the jugular vein with a glucose load of 60 mu mol/min kg, administered at the same time as 6-3H glucose and H14CO3-1. The three infusion conditions include (1) fasted 24 hours, (2) fasted 24 hours and run to exhaustion, and (3) fasted 24 hours and running at a rate of 20 m/min. After infusion for 2 hours, animals will be killed, and heart, liver and red and white portions of gastrocnemius muscles will be freeze-clamped. Blood glucose and lactate concentrations will be measured as well as the specific activities (SA) of 3H glucose, 14C glucose, 3H-lactate, and 14C-lactate. Total glycogen and 3H SA and 14C SA of glycogen in each of the isolated tissues will be determined. Activities of hexokinase, glucokinase, and glucose-6-phosphatase will be assayed in liver tissue. This research will lead to an increased knowledge of gluconeogenic rates and glycogenesis in trained animals.